System and method for introducing tissue stimulation lead into patient using real-time coupling efficiency measurements

ABSTRACT

A system and method for locating an implantable tissue stimulation lead within a patient. A measurement indicative of a coupling efficiency between the tissue stimulation lead and tissue at a location is taken. The location of the tissue stimulation lead relative to the tissue is tracked. Coupling efficiency information based on the measurement from the monitoring device is generated, tracking information based on the tissue stimulation lead location is generated, and the coupling efficiency information and tracking information is concurrently conveyed to the user.

RELATED APPLICATION DATA

The present application claims the benefit under 35 U.S.C. §119 to U.S.provisional patent application Ser. No. 61/405,535, filed Oct. 21, 2010.The foregoing application is hereby incorporated by reference into thepresent application in its entirety.

FIELD OF THE INVENTION

The present invention relates to tissue stimulation systems, and moreparticularly, to apparatus and methods for introducing tissuestimulation leads into patients.

BACKGROUND OF THE INVENTION

Implantable tissue stimulation systems have proven therapeutic in a widevariety of diseases and disorders. Pacemakers and Implantable CardiacDefibrillators (ICDs) have proven highly effective in the treatment of anumber of cardiac conditions (e.g., arrhythmias). Spinal CordStimulation (SCS) systems have long been accepted as a therapeuticmodality for the treatment of chronic pain syndromes, and theapplication of tissue stimulation has begun to expand to additionalapplications such as angina pectoralis and incontinence. Deep BrainStimulation (DBS) has also been applied therapeutically for well over adecade for the treatment of refractory chronic pain syndromes, and DBShas also recently been applied in additional areas such as movementdisorders and epilepsy. Further, Functional Electrical Stimulation (FES)systems such as the Freehand system by NeuroControl (Cleveland, Ohio)have been applied to restore some functionality to paralyzed extremitiesin spinal cord injury patients. Furthermore, in recent investigationsPeripheral Nerve Stimulation (PNS) systems have demonstrated efficacy inthe treatment of chronic pain syndromes and incontinence, and a numberof additional applications are currently under investigation. OccipitalNerve Stimulation (ONS), in which leads are implanted in the tissue overthe occipital nerves, has shown promise as a treatment for variousheadaches, including migraine headaches, cluster headaches, andcervicogenic headaches.

These implantable tissue stimulation systems typically include one ormore electrode carrying stimulation leads, which are implanted at thedesired stimulation site, and a neurostimulator (e.g., an implantablepulse generator (IPG)) implanted remotely from the stimulation site, butcoupled either directly to the tissue stimulation lead(s) or indirectlyto the tissue stimulation lead(s) via a lead extension. Thus, electricalpulses can be delivered from the neurostimulator to the tissuestimulation leads to stimulate the tissue and provide the desiredefficacious therapy to the patient. The tissue stimulation system mayfurther comprise a handheld patient programmer in the form of a remotecontrol (RC) to remotely instruct the neurostimulator to generateelectrical stimulation pulses in accordance with selected stimulationparameters. A typical stimulation parameter set may include theelectrodes that are acting as anodes or cathodes, as well as theamplitude, duration, and rate of the stimulation pulses. The RC may,itself, be programmed by a clinician, for example, by using aclinician's programmer (CP), which typically includes a general purposecomputer, such as a laptop, with a programming software packageinstalled thereon. Typically, the RC can only control theneurostimulator in a limited manner (e.g., by only selecting a programor adjusting the pulse amplitude or pulse width), whereas the CP can beused to control all of the stimulation parameters, including whichelectrodes are cathodes or anodes.

In the context of an SCS procedure, one or more stimulation leads areintroduced through the patient's back into the epidural space, such thatthe electrodes carried by the leads are arranged in a desired patternand spacing to create an electrode array. One type of commerciallyavailable stimulation leads is a percutaneous lead, which comprises acylindrical body with ring electrodes, and can be introduced intocontact with the affected spinal tissue through a Touhy-like needle,which passes through the skin, between the desired vertebrae, and intothe epidural space above the dura layer. For unilateral pain, apercutaneous lead is placed on the corresponding lateral side of thespinal cord. For bilateral pain, a percutaneous lead is placed down themidline of the spinal cord, or two or more percutaneous leads are placeddown the respective sides of the midline of the spinal cord, and if athird lead is used, down the midline of the spinal cord. After properplacement of the tissue stimulation leads at the target area of thespinal cord, the leads are anchored in place at an exit site to preventmovement of the tissue stimulation leads. To facilitate the location ofthe neurostimulator away from the exit point of the tissue stimulationleads, lead extensions are sometimes used.

The tissue stimulation leads, or the lead extensions, are then connectedto the IPG, which can then be operated to generate electrical pulsesthat are delivered, through the electrodes, to the targeted tissue, andin particular, the dorsal column and dorsal root fibers within thespinal cord. The stimulation creates the sensation known as paresthesia,which can be characterized as an alternative sensation that replaces thepain signals sensed by the patient. Intra-operatively (i.e., during thesurgical procedure), the neurostimulator may be operated to test theeffect of stimulation and adjust the parameters of the stimulation foroptimal pain relief. The patient may provide verbal feedback regardingthe presence of paresthesia over the pain area, and based on thisfeedback, the lead positions may be adjusted and re-anchored ifnecessary. A computer program, such as Bionic Navigator®, available fromBoston Scientific Neuromodulation Corporation, can be incorporated in aclinician's programmer (CP) (briefly discussed above) to facilitateselection of the stimulation parameters. Any incisions are then closedto fully implant the system. Post-operatively (i.e., after the surgicalprocedure has been completed), a clinician can adjust the stimulationparameters using the computerized programming system to re-optimize thetherapy.

The efficacy of SCS is related to the ability to stimulate the spinalcord tissue corresponding to evoked paresthesia in the region of thebody where the patient experiences pain. Thus, the working clinicalparadigm is that achievement of an effective result from SCS depends onthe tissue stimulation lead or leads being placed in a location (bothlongitudinal and lateral) relative to the spinal tissue such that theelectrical stimulation will induce paresthesia located in approximatelythe same place in the patient's body as the pain (i.e., the target oftreatment). If a lead is not correctly positioned, it is possible thatthe patient will receive little or no benefit from an implanted SCSsystem. Thus, correct lead placement can mean the difference betweeneffective and ineffective pain therapy, and as such, precise positioningof the leads proximal to the targets of stimulation is critical to thesuccess of the therapy.

One important parameter that can influence the electrical fieldgenerated by stimulation electrodes, and thus the proper placement ofthe leads, is the electrical conductivity environment due to the tissuecharacteristics surrounding the electrodes. This is often a secondaryconcern to the clinician, who will typically place the tissuestimulation leads based on anatomic (fluoroscopy, ultrasound, etc.) andphysiologic (compound action potentials, EMG, etc.) landmarks, and thenanticipate that the electrical environment seen by the electrodes willpromote good coupling efficiency between the tissue stimulation leadsand the target tissue, and will therefore not significantly affect thestimulation therapy.

However, it cannot always be assumed that the coupling efficiency is ata level high enough to achieve optimum performance even when theposition of the tissue stimulation leads relative to the tissue appearsto promote good coupling efficiency under conventional imaging. Forexample, in the case of SCS, when the tissue stimulation leads areviewed in the epidural space of the patient under a conventionalanterior fluoroscopic image, the leads may appear properly locatedrelative to the spinal cord. In reality, however, portions of the tissuestimulation leads may be dorsally located from the spinal cord arelatively far distance, which will not be appreciated from aconventional anterior fluoroscopic image. As a result, the couplingefficiency between the electrodes of the tissue stimulation leads thatare relatively far from the spinal cord may be quite low, which mayadversely affect the performance of the tissue stimulation system.

For example, in single-source tissue stimulation systems, the impedanceseen at each electrode may influence the amount of electrical currentthat can be delivered from each electrode, and thereby shape theelectrical field in a non-controllable manner. If the impedance is highenough, coupling efficiency between the electrodes and the target tissueto be stimulated will be so low that stimulation performance will besignificantly degraded. Even for multi-source tissue stimulation systemsthat precisely control the magnitude of electrical current at eachelectrode, the occurrence of a low coupling efficiency between theelectrodes and the surrounding tissue due to high electrode impedance,forces the system to use more energy that what would otherwise benecessary to maintain stimulation performance. As a result, an excessiveamount of compliance voltage may need to be generated in order toeffectively supply stimulation energy to the electrodes if the tissuestimulation system uses current-controlled sources, thereby resulting inan inefficient use of the battery power, or the stimulation energysupplied to the electrode may be otherwise inadequate if the tissuestimulation system uses voltage-controlled sources.

There, thus, remains a need for a system and method for positioningtissue stimulation leads within a tissue region of the patient thatprovides a suitable electrical conductivity environment for optimizingthe conveyance of electrical stimulation energy from the tissuestimulation leads.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present inventions, a systemfor locating an implantable tissue stimulation lead within a patient isprovided.

The system comprises a monitoring device configured for taking ameasurement indicative of a coupling efficiency between the tissuestimulation lead and tissue at a location. In one embodiment, themonitoring device is configured for taking the measurement by conveyingan electrical signal between the tissue stimulation lead and the tissue,and measuring an electrical parameter (e.g., an impedance or fieldpotential) in response to the conveyance of the electrical signal. In anoptional embodiment, the monitoring device is a neurostimulator furtherconfigured for delivering stimulation energy to the implantable tissuestimulation lead.

The system further comprises a tracking system configured for trackingthe location of the tissue stimulation lead relative to the tissue, andan external control device configured for generating coupling efficiencyinformation based on the measurement from the monitoring device, forgenerating tracking information based on the tissue stimulation leadlocation, and concurrently displaying the coupling efficiencyinformation (e.g., as one or more numerical values or one or moregraphs) and tracking information to the user.

In one embodiment, the tissue stimulation lead is configured for beingintroduced within the patient at different locations along a trajectorypath. In this case, the monitoring device may be configured for takingmeasurements indicating the coupling efficiencies between the tissuestimulation lead and the tissue at the different locations, the trackingsystem may be configured for tracking the different locations of thetissue stimulation lead, and the external control device may beconfigured for generating the coupling efficiency information based onthe measurements from the monitoring device, and for generating thetracking information based on the tissue stimulation lead locations. Thedisplayed tracking information may concurrently indicate the differentlocations of the tissue stimulation lead relative to the tissue. Thetracking information may be indicative of the different locations of thetissue stimulation lead relative to an anatomical structure of thepatient.

In accordance with a second aspect of the present inventions, anexternal control device for use with an implantable tissue stimulationlead, a monitoring device configured for taking a measurement indicativeof coupling efficiency between the tissue stimulation lead and tissue,and a tracking system configured for tracking a location of the tissuestimulation lead relative to the tissue, is provided.

The external control device comprises input circuitry configured forobtaining the measurement from the monitoring device and the tissuestimulation lead location from the tracking system. The external controldevice further comprises processing circuitry configured for generatingcoupling efficiency information based on the measurement received by theinput circuitry, for generating tracking information based on the tissuestimulation lead location received by the input circuitry, and forintegrating the coupling efficiency information and tracking informationtogether. The external control device further comprises a user interfaceconfigured for displaying the integrated coupling efficiency information(e.g., as one or more numerical values or one or more graphs) andtracking information.

In accordance with a third aspect of the present inventions, a method ofimplanting a tissue stimulation lead within tissue of a patient isprovided.

The method comprises advancing the tissue stimulation lead within thepatient at different locations along a trajectory path (e.g., within anepidural space of the patient), and generating coupling efficiencyinformation indicative of coupling efficiencies between the tissuestimulation lead and the tissue when the tissue stimulation lead isrespectively at the different locations. One method the couplingefficiency information is generated by conveying electrical signalsbetween the tissue stimulation lead and tissue of the patient when thetissue stimulation lead is at the different locations, and measuringelectrical parameters (e.g., an impedance or a field potential) inresponse to the conveyance of the electrical signals.

The method further comprises conveying the coupling efficiencyinformation to a user (e.g., by displaying the coupling efficiencyinformation), and affixing the tissue stimulation lead at a suitable oneof the different locations based on the coupling efficiency informationconveyed to the user. In one method, the suitable location is thelocation at which the coupling efficiency information indicates thecoupling efficiency between the tissue stimulation lead and the tissueas being the highest.

The tissue stimulation lead may carry a plurality of electrodes, inwhich case, the method may comprise determining raw coupling efficiencydata between the electrodes and the tissue when the tissue stimulationlead is at each of the different locations, and the coupling efficiencyinformation between the tissue stimulation lead and the tissue may bederived from the determined raw coupling efficiency data. After thetissue stimulation lead is placed at each location, the measurements andprocessing are preferably performed in real-time. That is, the timeelapsed between the placement of the tissue stimulation lead at each ofthe different locations along the trajectory path and the conveyance ofthe coupling efficiency information at each respective location is lessthan one second.

Another method further comprises generating tracking informationindicative of the different locations of the tissue stimulation lead,and displaying the tracking information with the coupling efficiencyinformation. The coupling efficiency information may be, e.g., one ormore numerical values or one or more graphs. In this case, the displayedtracking information may optionally concurrently indicate the differentlocations of the tissue stimulation lead. The tracking information maybe indicative of the different locations of the tissue stimulation leadrelative to an anatomical structure of the patient.

An optional method further comprises conveying stimulation energy fromthe tissue stimulation lead into the tissue at the different locationsalong the trajectory path;, and performing a corrective action (e.g.,repositioning the tissue stimulation lead or adjusting at least onestimulation parameter of the conveyed stimulation energy) if thecoupling efficiency information conveyed to the user indicates thecoupling efficiency between the tissue stimulation lead and the tissueas being low at one of the different locations.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is block diagram of a spinal cord stimulation (SCS) systemarranged in accordance with the present inventions;

FIG. 2 is a perspective view of the SCS system of FIG. 1;

FIG. 3 is a plan view of an implantable pulse generator (IPG) and twopercutaneous tissue stimulation leads used in the SCS system of FIG. 1;

FIG. 4 is a plan view of the SCS system of FIG. 1 in use with a patient;

FIGS. 5A-5C are plan views of a tissue stimulation lead being introducedwithin the epidural space of the patient at three different locations;

FIGS. 6A-6C are plan views of displays generated by a clinicianprogrammer of the SCS system of FIG. 1, particularly showing leadcoupling efficiency information in the form of numerical values;

FIGS. 7A-7C are plan views of displays generated by a clinicianprogrammer of the SCS system of FIG. 1, particularly showing leadcoupling efficiency information in the form of a bar graph; and

FIG. 8 is a plan view of a display generated by a clinician programmerof the SCS system of FIG. 1, particularly showing lead couplingefficiency information in the form of a line graph.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The description that follows relates to a spinal cord stimulation (SCS)system. However, it is to be understood that while the invention lendsitself well to applications in SCS, the invention, in its broadestaspects, may not be so limited. Rather, the invention may be used withany type of implantable electrical circuitry used to stimulate tissue.For example, the present invention may be used as part of a multi-leadsystem such as a pacemaker, a defibrillator, a cochlear stimulator, aretinal stimulator, a stimulator configured to produce coordinated limbmovement, a cortical stimulator, a deep brain stimulator, peripheralnerve stimulator, microstimulator, or in any other neural stimulatorconfigured to treat urinary incontinence, sleep apnea, shouldersublaxation, headache, etc.

Turning first to FIGS. 1-3, an exemplary SCS system 10 arranged inaccordance with one embodiment of the present inventions will bedescribed. The system 10 comprises components that may be subdividedinto three broad categories: (1) implantable components 12; (2) externalcomponents 14; and (3) surgical components 16. The implantablecomponents 12 include an implantable neurostimulator in the form of animplantable pulse generator (IPG) 18, one or more tissue stimulationleads 20 carrying an array of electrodes 22 (shown in FIG. 2), and alead extension 24 (as needed).

In the illustrated embodiment, the tissue stimulation leads 20 arepercutaneous leads, and to this end, the electrodes 22 are arrangedin-line along the tissue stimulation leads 20. Alternatively, the tissuestimulation leads 20 may be replaced with a single paddle stimulationlead. In the illustrated embodiment shown in FIG. 3, the firststimulation lead 20(1) has eight electrodes 22 (labeled E1-E8), and thesecond stimulation lead 20(2) includes eight electrodes 22 (labeledE9-E16). The actual number of leads and electrodes will, of course, varyaccording to the intended application.

The IPG 18 can provide electrical stimulation through at least some ofthe sixteen electrodes El through E16 included within the electrodearray 22. To this end, the IPG 18 may be connected directly to thetissue stimulation leads 20, or indirectly to stimulation leads 20 viathe lead extension 24. The IPG 18 includes stimulating electricalcircuitry, processing circuitry, a power source (e.g., a rechargeablebattery) or receiver, and telemetry circuitry, all contained within ahermetically sealed, biocompatible, case.

As shown in FIG. 4, the implantable components 12, which includes theIPG 18, the tissue stimulation lead(s) 20, and if needed, the leadextension(s) 24 may be implanted within a patient 60 using the surgicalcomponents 16, which include an insertion tool, such as a hollow needle28, a guidewire or stylet 30, and tunneling tools 32 (shown in FIG. 1).The tissue stimulation lead(s) 20 may be percutaneously implanted withinthe spinal column 62 of the patient 60 through the use of the needle 28and the stylet 30. The preferred placement of the tissue stimulationleads 20 is such that the electrode array 22 is adjacent (i.e., restingupon) the dura nearest the target area of the spinal cord 64 to bestimulated. For example, the needle 28 with stylet 30 is insertedthrough the back into the epidural space 66 of the patient 60. Thestylet 30 is then removed from the needle 28 to create a hollow opening,and a syringe (not shown) is inserted in the needle 28 to inject saline(3-5 cc) to ensure the needle tip has entered the epidural space 66. Oneof the tissue stimulation leads 20 is then passed through the needle 28into the epidural space 66. The other stimulation lead 20 is introducedinto the epidural space 66 in the same manner. After the tissuestimulation leads 20 are placed, the needle 28 is then pulled out, andan anchor (not shown) is placed around the tissue stimulation leads 20at the exit site and sutured in place to prevent movement of the tissuestimulation leads 20.

Due to the lack of space near the location where the tissue stimulationleads 20 exit the spinal column 62, the selected IPG 18 is generallyimplanted in a surgically-made pocket either in the abdomen or above thebuttocks. The IPG 18 may, of course, also be implanted in otherlocations of the patient's body. The lead extension(s) 24 facilitatelocating the IPG 18 away from the exit point of the tissue stimulationlead(s) 20. The lead extension(s) 24, for example, may be tunneled fromthe implantation site of the IPG 18 up to the spinal column 62 using thetunneling tools 32.

Electrical stimulation is provided by the IPG 18 to the electrode array22 in accordance with a set of stimulation parameters. Such stimulationparameters may comprise electrode combinations, which define theelectrodes that are activated as anodes (positive), cathodes (negative),and turned off (zero), and electrical pulse parameters, which define thepulse amplitude (measured in milliamps or volts depending on whether theIPG 18 supplies constant current or constant voltage to the electrodearray 22), pulse duration (measured in microseconds), and pulsefrequency (measured in pulses per second, or Hertz). Electricalstimulation of the tissue will occur between two (or more) electrodes,one of which may be the case of the IPG 18, a patch electrode, or thelike.

The IPG 18 may deliver stimulation energy to the electrode array 22 inany one or more different manners. For example, the IPG 18 may becapable of independently delivering constant current to the electrodesof the array 22 over multiple channels in either a multipolar ormonopolar manner; delivering constant current to the electrodes of thearray 22 over only a single channel in only a monopolar manner, oruniformly delivering constant voltage over multiple channels in either amultipolar or monopolar manner.

Significantly, the IPG 18 is capable of taking measurements that areindicative of the coupling efficiencies between the electrode array 22and the surrounding tissue. Notably, in the case of SCS, the electrodearray 22 fits snugly within the epidural space 66 of the spinal column62, and because the tissue is conductive, there is an impedanceassociated therewith that indicates how easily current flowstherethrough. Thus, the electrode impedance can be measured in order todetermine the coupling efficiency between the respective electrode array22 and the tissue. Other electrical parameter data, such as fieldpotential and evoked action potential, may also be measured toultimately determine the coupling efficiency between the electrodes 26and the tissue.

Electrical data can be measured using any one of a variety means. Forexample, the electrical data measurements can be made on a sampled basisduring a portion of the time while the electrical stimulus pulse isbeing applied to the tissue, or immediately subsequent to stimulation,as described in U.S. patent application Ser. No. 10/364,436, which haspreviously been incorporated herein by reference. Alternatively, theelectrical data measurements can be made independently of the electricalstimulation pulses, such as described in U.S. Pat. Nos. 6,516,227 and6,993,384, which are expressly incorporated herein by reference. Forexample, electrical data measurements can be made in response toalternating current (AC) or pulsatile electrical signals, whichpreferably use amplitudes and pulsewidths (e.g., 1 mA for 20 μs) thatgenerate no physiological response for the patient (i.e., subthreshold),but can alternatively be performed in response to stimulation pulses.

The impedance measurement technique may be performed by measuringimpedance vectors, which can be defined as impedance values measuredbetween selected pairs of electrodes 22. The interelectrode impedancemay be determined in various ways. For example, a known current (in thecase where the IPG 18 is sourcing current) can be applied between a pairof electrodes 22, a voltage between the electrodes 22 can be measured,and an impedance between the electrodes 22 can be calculated as a ratioof the measured voltage to known current. Or a known voltage (in thecase where the IPG is sourcing voltage) can be applied between a pair ofelectrodes 22, a current between the electrodes 22 can be measured, andan impedance between the electrodes 22 can be calculated as a ratio ofthe known voltage to measured current.

The field potential measurement technique may be performed by generatingan electrical field at selected ones of the electrodes 22 and recordingthe electrical field at other selected ones of the lead electrodes 22.This may be accomplished in one of a variety of manners. For example, anelectrical field may be generated conveying electrical energy to aselected one of the electrodes 22 and returning the electrical energy atthe IPG case. Alternatively, multipolar configurations (e.g., bipolar ortripolar) may be created between the lead electrodes 22. Or, anelectrode that is sutured (or otherwise permanently or temporarilyattached (e.g., an adhesive or gel-based electrode) anywhere on thepatient's body may be used in place of the case IPG outer case or leadelectrodes 22. In either case, while a selected one of the electrodes 22is activated to generate the electrical field, a selected one of theelectrodes 22 (different from the activated electrode) is operated torecord the voltage potential of the electrical field.

The evoked potential measurement technique may be performed bygenerating an electrical field at one of the electrodes 22, which isstrong enough to depolarize the neurons adjacent the stimulatingelectrode beyond a threshold level, thereby inducing the firing ofaction potentials (APs) that propagate along the neural fibers. Suchstimulation is preferably supra-threshold, but not uncomfortable. Asuitable stimulation pulse for this purpose is, for example, 4 mA for200 μS. While a selected one of the electrodes 22 is activated togenerate the electrical field, a selected one or ones of the electrodes22 (different from the activated electrode) is operated to record ameasurable deviation in the voltage caused by the evoked potential dueto the stimulation pulse at the stimulating electrode.

Further details discussing the measurement of electrical parameter data,such as electrode impedance, field potential, and evoked actionpotentials, as well as other parameter data, such as pressure,translucence, reflectance and pH (which can alternatively be used), todetermine the coupling efficiency between an electrode and tissue areset forth in U.S. patent application Ser. No. 10/364,436, entitled“Neural Stimulation System Providing Auto Adjustment of Stimulus Outputas a Function of Sensed Impedance,” U.S. patent application Ser. No.10/364,434, entitled “Neural Stimulation System Providing AutoAdjustment of Stimulus Output as a Function of Sensed Pressure Changes,”U.S. Pat. No. 6,993,384, entitled “Apparatus and Method for Determiningthe Relative Position and Orientation of Tissue stimulation leads,” andU.S. patent application Ser. No. 11/096,483, entitled “Apparatus andMethods for Detecting Migration of Tissue stimulation leads,” which areexpressly incorporated herein by reference.

Thus, it can be appreciated from the foregoing, that as each tissuestimulation lead 20 is introduced within the patient at differentlocations along a trajectory path, and in the case of SCS along theepidural space 66 of the patient 60, the IPG 18 can take measurementsindicative coupling efficiencies between each of the electrodes 22 (andthus the tissue stimulation leads 20) and the tissue at the differentlocations. Although the measurement of parameters indicative of leadcoupling efficiency have been described as being taken by the IPG 18, itshould be appreciated that such measurements can be alternatively takenby any monitoring device capable of measuring and communicating couplingefficiency indicating parameters to an external control device.

Referring still to FIGS. 1 and 2, the external components 14 may includean external trial stimulator (ETS) 34, an external charger 36, acharging port 38, a hand-held programmers (HHP) 40, a cliniciansprogrammer station (CPS) 42, percutaneous lead extension(s) 44 (ifneeded), and external cable(s) 46, and a tracking system 48.

The ETS 34 is capable of being used on a trial basis for a period oftime (e.g., 7-14 days) after the tissue stimulation lead(s) 20 have beenimplanted, and prior to implantation of the IPG 18, to test theeffectiveness of the stimulation that is to be provided. The tissuestimulation lead(s) 20 may be connected to the ETS 34 (via one or moreconnectors on the ETS 34) through the use of the lead extension(s) 44and external cable(s) 46. The ETS 34 essentially operates in the samemanner as the IPG 18 in that it can provide stimulation energy to theelectrodes 22 and take measurements indicative of the couplingefficiency between the tissue stimulation leads 22 and the surroundingtissue.

When needed, an external charger 36 is non-invasively coupled with theIPG 18 through a communications link 50, e.g., an inductive link,allowing energy stored or otherwise made available to the charger 36 viathe charging port 38 to be coupled into a rechargeable battery housedwithin the IPG 18. The HHP 40 may be used to control the IPG 18 via asuitable non-invasive communications link 52, e.g., an RF link. Suchcontrol allows the IPG 18 to be turned on or off, and generally allowsstimulation parameters to be set within prescribed limits. The HHP 40may also be linked with the ETS 34 through another communications link54, e.g., an RF link, to likewise set stimulation parameters withinprescribed limits. Thus, the HHP 40 is considered to be in“telecommunicative” contact with the IPG 18 or ETS 34.

The tracking system 48 is capable of tracking the location of theelectrodes 22 on each tissue stimulation lead 20 relative to ananatomical structure, and in this case, the spinal column 62 of thepatient 60 (shown in FIG. 4). The tracking system 48 may take the formof any conventional tracking system, such as a signaling system (e.g., aradio frequency (RF) triangulation or a multiple-dimension ultrasonicpositioning system) or a conventional imaging system (e.g., a real-timecomputed tomography (CT) or fluoroscopic machine). In the case of asignaling tracking system, one or more transducers (which may be theelectrodes 22 themselves) may be located on the tissue stimulation leads20 and positioning signals can transmitted between these transducers andan external positioning system, such that the locations of theelectrodes 22 and the anatomical reference can be determined in athree-dimensional coordinate system. If the signaling transducers arelocated on the tissue stimulation leads 20 a distance from theelectrodes 22, the locations of the electrodes 22 can simply bedetermined from the known distances between the electrodes 22 and theknown location of the transducer or transducers relative to one of theelectrodes 22. In any event, as each tissue stimulation lead 20 isintroduced within the patient at different locations along a trajectorypath, and in the case of SCS along the epidural space 66 of the patient60, the tracking system 48 can track the electrodes 22 of the tissuestimulation lead 20 at different locations relative to the spinal column62 of the patient 60.

Modifying the stimulation parameters in the programmable memory of theIPG 14 after implantation (or in the ETS 34) may be performed by aphysician or clinician using the CPS 42, which can directly communicatewith the IPG 18 or indirectly communicate with the IPG 18 via the HHP40. That is, the CPS 42 can be used by the physician or clinician tomodify parameters of the stimulation pulses delivered by electrode array22 near the spinal cord. In the illustrated embodiment, the CPS 42 islinked to the HHP 40 via another communications link 56, e.g., an infrared link. Alternatively, the CPS 42 can be coupled directly to the IPG18 or ETS 34 via a communications link (not shown) or cable. Thus, theCPS 42 is considered to be in “telecommunicative” contact with the IPG18 or ETS 34. The CPS 42 is also linked to the tracking system 48 via acommunications link 58, e.g., a cable.

The overall appearance of the CPS 42 is that of a laptop personalcomputer (PC). Thus, in this embodiment illustrated in FIG. 4, the CPS42 includes a user input device 68 (e.g., a keyboard, joystick, and amouse) and a display (e.g., monitor, LED array, or the like) 70 housedin a case. The CPS 42 also comprises a processor (not shown) configuredfor performing the functions described below for the CPS 42, and inputcircuitry (not shown) configured for receiving information (e.g.,measurements) from the IPG 18 over communications link 56 and forreceiving information (e.g., tissue stimulation lead locations) from thetracking system 48 over communications link 57. The programmingmethodologies can be performed by executing software instructions in theprocessor contained within the CPS 42. Alternatively, such programmingmethodologies can be performed using firmware or hardware.

In any event, the CPS 42 may actively control the characteristics of theelectrical stimulation generated by the IPG 18 (or ETS 34) to allow theoptimum stimulation parameters to be determined based on patientfeedback and for subsequently programming the IPG 18 (or ETS 34) withthe optimum stimulation parameters.

Significantly, based on the measurements obtained from the IPG 18, theCPS 42 is configured for generating coupling efficiency information(i.e., information indicative of the coupling efficiency between thetissue stimulation lead 20 and tissue) for each of the locations atwhich the tissue stimulation lead 20 is placed, and based on the leadlocation information obtained from the tracking system 48, the CPS 42 isconfigured for generating lead location information (i.e., informationindicative of the tracked location of the tissue stimulation leadrelative to the spinal column 62 of the patient 60).

The coupling efficiency information may be derived from the measurementstaken by the IPG 18 in any one or more of a variety of manners. Forexample, the coupling efficiency information for the tissue stimulationlead 20 may simply comprise the individual coupling efficiencies (e.g.,impedance values, field potential values, etc.) between the respectiveelectrodes 22 and the tissue. Of course, if the coupling efficiencybetween only one of the electrodes 22 and the tissue is available, thenthe coupling efficiency for the tissue stimulation lead 20 will comprisethis single individual coupling efficiency for that electrode 22.Alternatively, the coupling efficiency information for the tissuestimulation lead 20 may be an average of the individual couplingefficiencies between the respective electrodes 22 and the tissue, theminimum of the individual coupling efficiencies between the respectiveelectrodes 22, or the maximum of the individual coupling efficienciesbetween the respective electrodes 22. For each location of the tissuestimulation lead 20, the coupling efficiency information may comprise anabsolute value or absolute values, or alternatively, the couplingefficiency information may comprise normalized or relative values forthe locations of the tissue stimulation lead 20 that allow the user tocompare them to get a sense of sufficient or insufficient couplingefficiencies. The displayed coupling efficiency information may benumerical or may take the form of a graph (e.g., a line graph or bargraph).

The tracking information may take any form that allows the user to gaugewhere the electrodes 22 are relative to the spinal column 62 of thepatient 60. In the case where the tracking system 48 is a conventionalimaging system, such as a fluoroscope or CT, the displayed trackinginformation may simply be the image of the electrodes 22 and surroundingstructure of the spinal column. In the case where the tracking system 48is, e.g., an RF triangulation or ultrasonic positioning system, the CPS42 graphically generate representations of the electrodes 22 that may besuperimposed over a pre-operative image of the spinal column 62 of thepatient 60, or alternatively over an image of a spinal column 62obtained from an atlas.

The CP 18 is configured for integrating the coupling efficiencyinformation and tracking information together, so that they can beconcurrently displaced together on the same screen. If the couplingefficiency information for the tissue stimulation lead 20 comprises aplurality of coupling efficiencies for the respective electrodes 22, theindividual coupling efficiencies are preferably displayed adjacent tothe respective electrodes 22, so that the user can easily associate eachcoupling efficiency with the respective electrode 22 with which it isassociated. If the coupling efficiency information for the tissuestimulation lead 20 comprises a single coupling efficiency, then thesingle coupling efficiency may be displaced adjacent the determinedlocation of the tissue stimulation lead 20. In an optional embodiment,the CPS 42 may concurrently display the coupling efficiency informationfor more than one location of the tissue stimulation lead 20, therebyproviding a history of the coupling efficiency information in a singledisplay screen.

With reference to FIGS. 5-8, methods of delivering a tissue stimulationlead 20 into the proper location in the epidural space 66 of the patient60 will now be described. First, the tissue stimulation lead 20 isconnected to the IPG 18 as it is outside the patient, the ETS 34, or anyother monitoring device capable of measuring a parameter indicative ofthe coupling efficiency between the tissue stimulation lead 20 and thesurrounding tissue.

As the clinician or physician advances the tissue stimulation lead 20along a trajectory path in the epidural space 66, the tissue stimulationlead 20 is placed in different locations relative to the spinal column62 of the patient 60, and in this case, location L1 (FIG. 5A), locationL2 (FIG. 5B), and location L3 (FIG. 5C) as identified by the distal tipof the tissue stimulation lead 20. Of course, the locations arearbitrary, and can thus be identified by any portion of the tissuestimulation lead 20.

During the advancement of the tissue stimulation lead 20 within theepidural space 66, the IPG 18 is operated to measure parametersindicative of the coupling efficiency between the tissue stimulationlead 20 and the tissue when the tissue stimulation lead 20 isrespectively at locations L1-L3. For example, the IPG 18 may conveyelectrical signals between tissue stimulation lead 20 and the tissuewhen the tissue stimulation lead 20 is respectively at locations L1-L3(e.g., respectively from electrodes E1-E16) and measuring electricalparameters (e.g., an impedance or field potential) in response to theconveyance of the electrical signals. Of course, as discussed above,there are many other types of parameters (electrical and non-electrical)indicative of the coupling efficiency between the tissue stimulationlead 20 and tissue that can be measured. The measured parameters, inessence, are determined raw coupling efficiency data between theelectrodes 22 and the tissue when the tissue stimulation lead 20 is ateach of the different locations L1-L3.

During the advancement of the tissue stimulation lead 20 within theepidural space 66, the tracking system 48 is also operated to determinethe location of the tissue stimulation lead 20 relative to an anatomicalreference, and in this, case the spinal column 62 of the patient 60. Asdiscussed above, the tracking system may acquire an image of the tissuestimulation lead 20 and anatomical reference or may determine thelocation of the tissue stimulation lead 20 at locations L1-L3 relativeto the spinal column 62 of the patient 60 in a three-dimensionalcoordinate system.

The CPS 42 obtains the raw coupling efficiency data between theelectrodes 22 and the tissue (i.e., the measured parameters) from theIPG 18, derives the coupling efficiency information from the rawcoupling efficiency data, e.g., in any of the manners described above.The CPS 42 also obtains the locations of the tissue stimulation lead 20relative to the spinal column 62 of the patient 60 from the trackingsystem 48, and in the case where the tracking system 48 is athree-dimensional positioning system, may involve graphically generatingrepresentations of the electrodes 22 and the spinal column 62 relativeto each other. In the case where the tracking system 48 is aconventional imaging system, the CPS 42 may simply regenerate theimaging data of the tissue stimulation lead 20 and spinal column 62.

The CPS 42 then conveys the coupling efficiency information and the leadlocation information to the user, and in the preferred embodiment,displays this information to the user. In one embodiment, the CPS 42displays the coupling efficiency information concurrently with the leadlocation information.

For example, as illustrated in FIGS. 6A-6C, the CPS 42 may display theelectrodes 22 while the leads 20 are respectively at locations L1 (FIG.6A), L2 (FIG. 6B), and L3 (FIG. 6C) and the corresponding couplingefficiencies of the tissue stimulation lead 20 at these respectivelocations. As there shown, the displayed coupling efficiencies take theform of a single field potential value displayed at the distal end ofthe tissue stimulation lead 20 for each location. Of course, asdiscussed above, the coupling efficiencies can take the form of anyindicator of a coupling efficiency. For example, as illustrated in FIGS.7A-7C, the coupling efficiencies may take the form of bar graphs thatare respectively associated with the electrodes 22. As shown in FIG. 8,the CPS 42 concurrently displays the different locations of the tissuestimulation lead 20 relative to the spinal column 62. In this case, theCPS 42 displays the coupling efficiencies (each of which is associatedwith a different location) as a line graph along the spinal column 62.

With knowledge of the coupling efficiency of the tissue stimulation lead20, the user will affix the tissue stimulation lead 20 at a suitable oneof the locations L1-L3, preferably the location at which the couplingefficiency between the tissue stimulation lead 20 and the tissue is thehighest. In an optional method, the user may operate the IPG 18 toconvey stimulation energy to the electrodes 22 and into the spinal cord66 as the tissue stimulation lead 20 is advanced within the epiduralspace 66 of the patient 60. As the tissue stimulation lead 20 is placedin different locations along the epidural space 66, the patient maysense paresthesia in different regions of the body. If the paresthesiais generally felt in the region requiring therapy, but is not effective,the user may determine the coupling efficiency from the display of theCPS 42, and if the coupling efficiency is low, the user may perform acorrective action. For example, the user reposition the tissuestimulation lead 20 within the epidural space 66 (e.g., a portion of thetissue stimulation lead 20 may be too far from the spinal cord 64 toprovide efficiency stimulation thereto) or may adjust the stimulationparameters (e.g., increasing the amplitude of the stimulation energy).

Preferably, after tissue stimulation lead 20 is placed at each of thelocations, the measurements and processing functions described hereinare performed in real-time. That is, the time elapsed between theplacement of the tissue stimulation lead 20 at each of the differentlocations L1-L3 along the trajectory path and the conveyance of thecoupling efficiency information to the user at each respective locationis less than one second.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

1. A system for locating an implantable tissue stimulation lead within apatient, comprising: a monitoring device configured for taking ameasurement indicative of a coupling efficiency between the tissuestimulation lead and tissue at a location; a tracking system configuredfor tracking the location of the tissue stimulation lead relative to thetissue; and an external control device configured for generatingcoupling efficiency information based on the measurement from themonitoring device, for generating tracking information based on thetissue stimulation lead location, and concurrently displaying thecoupling efficiency information and tracking information to the user. 2.The system of claim 1, wherein the monitoring device is aneurostimulator further configured for delivering stimulation energy tothe implantable tissue stimulation lead.
 3. The system of claim 1,wherein the monitoring device is configured for taking the measurementby conveying an electrical signal between the tissue stimulation leadand the tissue, and measuring an electrical parameter in response to theconveyance of the electrical signal.
 4. The system of claim 3, whereinthe measured electrical parameter is one of an impedance and a fieldpotential.
 5. The system of claim 1, wherein the tissue stimulation leadis configured for being introduced within the patient at differentlocations along a trajectory path, the monitoring device is configuredfor taking measurements indicating the coupling efficiencies between thetissue stimulation lead and the tissue at the different locations, thetracking system is configured for tracking the different locations ofthe tissue stimulation lead, and the external control device isconfigured for generating the coupling efficiency information based onthe measurements from the monitoring device, and for generating thetracking information based on the tissue stimulation lead locations. 6.The system of claim 5, wherein the displayed tracking informationconcurrently indicates the different locations of the tissue stimulationlead relative to the tissue.
 7. The system of claim 5, wherein thetracking information is indicative of the different locations of thetissue stimulation lead relative to an anatomical structure of thepatient.
 8. The system of claim 1, wherein the external control deviceis configured for displaying the coupling efficiency information as oneor more numerical values.
 9. The system of claim 1, wherein the externalcontrol device is configured for displaying the coupling efficiencyinformation as one or more graphs.
 10. An external control device foruse with an implantable tissue stimulation lead, a monitoring deviceconfigured for taking a measurement indicative of coupling efficiencybetween the tissue stimulation lead and tissue, and a tracking systemconfigured for tracking a location of the tissue stimulation leadrelative to the tissue, the external control device comprising: inputcircuitry configured for obtaining the measurement from the monitoringdevice and the tissue stimulation lead location from the trackingsystem; at least one processor configured for generating couplingefficiency information based on the measurement received by the inputcircuitry, for generating tracking information based on the tissuestimulation lead location received by the input circuitry, and forintegrating the coupling efficiency information and tracking informationtogether; and a user interface configured for displaying the integratedcoupling efficiency information and tracking information.
 11. Theexternal control device of claim 10, wherein the user interface isconfigured for displaying the coupling efficiency information as one ormore numerical values.
 12. The external control device of claim 10,wherein the user interface is configured for displaying the couplingefficiency information as one or more graphs.
 13. A method of implantinga tissue stimulation lead within tissue of a patient, comprising:advancing the tissue stimulation lead within the patient at differentlocations along a trajectory path; generating coupling efficiencyinformation indicative of coupling efficiencies between the tissuestimulation lead and the tissue when the tissue stimulation lead isrespectively at the different locations; conveying the couplingefficiency information to a user; and affixing the tissue stimulationlead at a suitable one of the different locations based on the couplingefficiency information conveyed to the user.
 14. The method of claim 13,further comprising conveying electrical signals between the tissuestimulation lead and tissue of the patient when the tissue stimulationlead is at the different locations, and measuring electrical parametersin response to the conveyance of the electrical signals, wherein thecoupling efficiency information is generated based on the measuredelectrical parameters.
 15. The method of claim 14, wherein each of themeasured electrical parameters is one of an impedance and a fieldpotential.
 16. The method of claim 13, wherein the suitable location isthe location at which the coupling efficiency information indicates thecoupling efficiency between the tissue stimulation lead and the tissueas being the highest.
 17. The method of claim 13, wherein the couplingefficiency information is displayed to the user.
 18. The method of claim17, further comprising: generating tracking information indicative ofthe different locations of the tissue stimulation lead; and displayingthe tracking information with the coupling efficiency information. 19.The method of claim 18, wherein the displayed tracking informationconcurrently indicates the different locations of the tissue stimulationlead.
 20. The method of claim 18, wherein the tracking information isindicative of the different locations of the tissue stimulation leadrelative to an anatomical structure of the patient.
 21. The method ofclaim 17, wherein the coupling efficiency information is displayed asone or more numerical values.
 22. The method of claim 17, wherein thecoupling efficiency information is displayed as one or more graphs. 23.The method of claim 13, wherein the tissue stimulation lead carries aplurality of electrodes, the method comprising determining raw couplingefficiency data between the electrodes and the tissue when the tissuestimulation lead is at each of the different locations, and the couplingefficiency information between the tissue stimulation lead and thetissue is derived from the determined raw coupling efficiency data. 24.The method of claim 13, wherein the time elapsed between the placementof the tissue stimulation lead at each of the different locations alongthe trajectory path and the conveyance of the coupling efficiencyinformation at each respective location is less than one second.
 25. Themethod of claim 13, wherein the trajectory path is within the epiduralspace of the patient.
 26. The method of claim 13, further comprising:conveying stimulation energy from the tissue stimulation lead into thetissue at the different locations along the trajectory path; andperforming a corrective action if the coupling efficiency informationconveyed to the user indicates the coupling efficiency between thetissue stimulation lead and the tissue as being low at one of thedifferent locations.
 27. The method of claim 26, wherein the correctiveaction is one or more of repositioning the tissue stimulation lead andadjusting at least one stimulation parameter of the stimulation energyconveyed from the tissue stimulation lead into the tissue.